Vol. 10(11) pp. 320-326, November 2016 DOI: 10.5897/AJFS2016.1471 Article Number: 5CAB0F260709 ISSN 1996-0794 African Journal of Food Science Copyright © 2016 Author(s) retain the copyright of this article http://www.academicjournals.org/AJFS

Full Length Research Paper

Evaluation of dry matter, starch and beta-carotene content in orange-fleshed sweet potato (Ipomoea batatas L.) genotypes tested in three agro-ecological zones of Malawi

D. M. Kathabwalika, E. H. C. Chilembwe and V. M. Mwale*

Lilongwe University of Agriculture and Natural Resources (LUANAR), Bunda College Campus, P.O.Box 219, Lilongwe, Malawi.

Received 31 May, 2016; Accepted 3 August, 2016

Evaluation of dry matter, starch, beta-carotene content and stability of eight orange-fleshed sweet potato genotypes was conducted at Bunda College in Malawi. Genotypes LU06/0527, LU06/0252, LU06/0428, LU06/0299, LU06/0258, BV/009, Kenya and Zondeni were evaluated. The genotypes were grown in three agro-ecological zones of Malawi namely Maseya in Chikhwawa District representing low altitude areas with hot climate; Bunda in Lilongwe District representing medium altitude with warm climate and Bembeke in Dedza District representing high altitude areas with cool climate. Harvested tubers were evaluated for dry matter, starch and beta-carotene content using spectrophotometry. Analysis of variance on the main effects between genotypes and environments as well as Interaction Principle Component Analysis (IPCA) for the residual multiplication interaction between genotypes and environments for beta-carotene content in the eight genotypes were conducted. Results showed significant differences in dry matter, starch and beta-carotene content among genotypes and across sites. Zondeni produced highest dry matter (34.4%) while BV/009 was the least (26.8%). Genotype LU06/0252 produced highest beta-carotene (6793.2 μg/100 g) followed by Zondeni (5620.9 μg/100 g). Beta-carotene content increased significantly with decreasing altitude and was highest at Maseya (4258.5 μg/100 g) followed by Bunda (3556.2 μg/100 g). Stability analysis showed that Kenya (SPN/O) was the most stable genotype in beta-carotene content across the sites. Bembeke was the most stable site while Maseya recorded highest beta-carotene content but was unstable site.

Key words: Orange-fleshed sweet potato, agro-ecological zones, beta-carotene content, starch content, dry matter content.

INTRODUCTION

Sweet potato (Ipomoea batatas L.) is an important root crop in sub-Saharan Africa (SSA) region and ranks

*Corresponding author. E-mail: [email protected].

Author(s) agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Kathabwalika et al. 321

Table 1. Description of locality and elevation in metres above sea level (masl) of the sites.

Average Elevation Average rainfall Study site Locality Soil type temperature (°C) (masl) (mm/annum) 16° 04’ S Maseya 29.5 Alfisols 200 600 34° 80’ E

14° 12’ S Bunda 20.0 Lithosols 1200 1030 33° 46’ E

14° 35’ E Bembeke 15.0 Lithosols 1600 1500 34° 43’ S

second after cassava in Malawi (Chipungu et al., 1999). three agro-ecological zones of Malawi. Sweetpotato are mainly grown for human consumption and take different forms according to a particular locality. MATERIALS AND METHODS In Malawi, both roots and leaves are extensively utilized. Traditionally, peeled roots are boiled and groundnuts Sites and farmers selection flour is added to produce local food product, futali. Sweet potato also forms part of the breakfast for the majority of The first phase of this study was conducted at three sites representing three different agro-ecological zones of Malawi. The both rural and urban dwellers in the country. Harvested sites were Bembeke in Dedza District representing the high altitude, leaves are also utilized as delicious relish when cooked cool and wet plateau zone, Bunda in Lilongwe District representing after adding groundnuts flour. middle altitude warm plain zone and Maseya in Chikhwawa District Use of orange fleshed sweet potato (OFSP) has representing low altitude hot and dry agro ecological zone (Table become a promising intervention in addressing vitamin A 1). Classification of the agro ecological zones was based on deficiency (VAD) which according to Kapinga et al. altitude, soil conditions, temperatures and amount of rainfall (Saka et al., 2006; Kathabwalika et al., 2013). (2010) is at 32% level of the population in sub-Saharan Three farmers were selected to carry out the study at each site Africa. This is mainly due to the fact that sweet potato within agro ecological zone. Planting and management of sweet already exists in consumer diets of most communities potato genotypes were reported in the previous study by and OFSP have wide acceptance among women and Kathabwalika et al. (2013). During harvesting, fifteen sweet potato children (Kapinga et al., 2010) who are at great risk of tubers for each genotype were randomly sampled and collected VAD (NSO, 2006). from each farmer’s field in the three agro-ecological zones where the genotypes were grown. The samples were transported under Despite this potential, Malawi as a country faces cool conditions for laboratory analysis to reduce dehydration. challenges in successfully benefiting from OFSP. One of the major challenges is lack of improved varieties as the Sweet potato genotypes used current literature indicates that over 95% of sweet potato produced in Malawi is white or cream fleshed (Chipungu, Eight promising orange fleshed sweet potato (OFSP) genotypes 2008). These varieties are also responsible for the low sourced from Kasinthula Agricultural Research Station namely. beta-carotene as well as dry matter contents (Brabet et LU06/0299, LU06/0258, LU06/527, BV/009, LU06/0252, LU06/0428, al., 1999; Carey et al., 1999; Chipungu, 2009). It is Zondeni and Kenya, were selected for evaluation of their dry matter, starch and beta-carotene contents. Zondeni and Kenya, against this background that a series of on-station and both released varieties, were used as checks for beta-carotene on-farm trials on elite orange fleshed sweet potato content. Table 2 shows descriptions of the genotypes. genotypes was conducted across the country to evaluate growth, yield stability as well as beta-carotene content Determination of dry matter, starch and β-carotene content (Chipungu, 2009; Kathabwalika et al., 2013). However, there are contradicting findings on trend of Dry matter content was determined by oven drying triplicates of 5 g beta-carotene content in OFSP grown at different samples at 80°C for 24 h and quantified as DM% = dry weight/fresh altitudes. Studies conducted elsewhere have shown that weight x 100 (Kwach et al., 2010; Yildirim et al., 2011). For beta- carotene content, five roots of each genotype were manually cut an increase in altitude leads to subsequent increase in into small pieces of about 1 cm and mixed. The pieces were beta-carotene (Manrique and Hermann, 2000; Ndirigwe homogenized rapidly (2-3 min) to prevent enzymatic degradation of et al., 2007). On the other hand, beta-carotene content carotenoids. Celite and petroleum ether (PE) were used for showed no clear trends with increasing or decreasing extraction and partitioning of beta-carotene from prepared samples altitude in Tanzania (Mbwaga et al., 2007). Additionally, to get the filtrate (Rodriguez-Amaya and Kimura, 2004; Ukpabi and such studies have not been conducted in Malawi. Ekeledo, 2009). The filtrate for each sample was put in 1 x 1 cm cuvette and Therefore, the aim of the study was to evaluate dry absorbance readings were taken at λ = 450 nm to determine beta- matter, starch and beta-carotene content in orange- carotene content using UV/Vis spectrophotometer (Jenway 6405) fleshed sweet potato (Ipomoea batatas L.) genotypes in and quantified as follows: beta-carotene (μg/100 g) = A x volume 322 Afr. J. Food Sci.

Table 2. Genotype source, growth habit, skin and flesh colours, maturity in months after planting (MAP) and potential yield (t/ha).

Maturity Potential yield Genotype Female parent/source Growth habit Skin colour Flesh colour (MAP) * (t/ha)* BV/009 LU96/374 Spreading Cream Deep orange 5 20-25 LU06/0252 Mafutha from RSA Spreading Purple Pale orange 5 25-30 LU06/0258 Kakoma (TIS 3017) from IITA Spreading Cream Yellow 5 20-25 LU06/0299 Kakoma (TIS 3017) Spreading Cream Yellow 5 20-25 LU06/0428 Mugamba (Mogamba, CIP, Nairobi) Spreading Cream Pale orange 3.5 30-35 LU06/0527 Kenya (SPN/O) Spreading Orange Orange 5 30-35 Kenya (SPN/O) Introduced cultivar Semi-erect Cream Pale yellow 4 to 5 25-30 Zondeni Local cultivar Erect Orange Deep orange 5 10-15

*Data obtained from on-station results during the initial stages of the genotypes evaluation

(ml) × 104/Ac × sample weight (g) where A is the used to carry out stability analysis of beta-carotene content highest percentage of starch (27.7%) followed by absorbance, volume is the total volume of extract and Ac is for the genotypes and environments. Bunda (22.4%), while Maseya had the lowest the absorption coefficient of beta-carotene in petroleum percentage (21.5%). Genotypes percentage and ether (2592). For starch extraction, five raw tubers from the interaction between sites and genotypes were each genotype were randomly sampled, washed clean and RESULTS peeled. The peeled sweet potato samples were sliced with not significantly different (p>0.05) (Table 4). Kenya a knife and ground into small pieces after recording their recorded the highest starch content (27.3%) initial weight. Thereafter, they were placed in a mixture of Dry matter content across the agro ecological zones while the lowest water and stirred for one to two minutes. The grinding starch percentage (23.5%) was recorded in process was repeated for three to four times till a The interaction between genotype and environ- homogenous suspension was obtained. The suspension ment was significant (p<0.001) on root dry matter. BV/009 and LU06/0252. was strained through fine cheesecloth into another beaker. Genotype LU06/0527 was the highest (34.4%) at Thereafter, the mixture was allowed to stand for few Bunda, while BV/009 was the least (23.3%) (Table minutes and then the deposition of starch was noted at the 3). Beta-carotene content bottom. The supernatant fluid was poured out and the beaker, containing the starch, was filled with water. The Genotype LU06/0428 was the highest at mixture was stirred well and allowed to settle. The process Bembeke with 34.1% followed by Zondeni with Beta carotene content was significantly different was repeated four to five times by separating starch that 33.7%, whereas Kenya was the lowest (27.5%). (p<0.001) across sites and among genotypes. can be washed thoroughly. The compact white starch The average dry matter content at Maseya was Beta carotene was highest at Maseya (4258.5 deposit was collected onto watch glass and dried in an 28.6% with Zondeni being the highest with 35.4%, μg/100 g) followed by Bunda (3556.2 μg/100 g), oven. After weighing the sample gravimetrically, the while LU06/0299 was the lowest with 22.5%. while Bembeke was the least (3104.2 μg/100 g). amount was converted into percentage over the initial weight of the extracted potato sample. However, Zondeni consistently produced highest Genotype LU06/0252 was the highest (6793.2 dry matter across sites with an average of 34.4%. μg/100 g) followed by Zondeni (5620.9 μg/100 g) and BV/009 (5066.9 μg/100 g) (Table 5). Data analysis Kenya variety was the lowest in beta-carotene content. The interaction between sites and geno- Data was analyzed using Genstat 14th Edition statistical Starch content package where analysis of variance (ANOVA) was done on types was significant (p<0.001). Genotype treatment means and Additive Main effects and Starch content showed significant differences LU06/0252 was the best performer at both Bunda Multiplicative Interaction (AMMI) model (Gauch, 1993) was (p<0.05) across sites. Bembeke recorded the and Bembeke, whereas BV/009 was the best at Kathabwalika et al. 323

Table 3. Dry matter (%) content of sweet potato genotypes Table 5. Beta-carotene content (µg/100 g) of orange-fleshed across sites. sweet potato genotypes across the study sites.

Site Site Genotype Mean Genotype Mean Bunda Bembeke Maseya Bunda Bembeke Maseya BV/009 23.3 31.7 25.5 26.8 BV/009 3441.3 4238.1 7521.3 5066.9 LU06/0252 27.5 31.5 29.9 29.7 LU06/0252 7869.9 5941.5 6568.3 6793.2 LU06/0258 31.2 31.5 23.5 28.7 LU06/0258 1480.7 1882.6 2695.1 2019.5 LU06/0299 28.2 29.9 22.5 26.9 LU06/0299 1241.2 649.4 2578.4 1489.7 LU06/0428 26.2 34.1 32.8 31.0 LU06/0428 6336.8 3234.3 3234.6 4235.2 LU06/0527 34.4 31.3 27.7 31.1 LU06/0527 2160.5 3542.9 3674.4 3125.9 Zondeni 34.0 33.7 35.4 34.4 Zondeni 5452.5 4446.3 6963.8 5620.9 Kenya 33.7 27.5 31.5 30.9 Kenya 467.0 898.3 932.2 765.8 Mean 28.8 31.4 28.6 30.0 Mean 3556.2 3104.2 4258.5 3639.64 Genotypes P<0.001 LSD 0.01 Genotypes P<0.001 LSD 77.7

Sites P<0.001 LSD 0.01 Sites P<0.001 LSD 47.6

G x E P<0.001 G x E P<0.001 LSD 0.03 LSD 134.6 CV (%) 5.2 CV (%) 2.3

Table 4. Starch content (%) of eight orange fleshed sweet used to explain the stability of beta-carotene. Genotypes potato genotypes across sites. LU06/0252, Zondeni, BV/009 and LU06/0428 contained higher beta-carotene than LU06/0258, LU06/0299, Site Genotype Mean LU06/0527 and Kenya. Bunda Bembeke Maseya Genotypes LU06/0428 and LU06/0252 showed negative BV/009 24.6 28.4 17.6 23.5 interactions while the rest had positive interactions (Figure LU06/0252 20.4 34.1 16.2 23.5 1). However, Zondeni, LU06/0527, LU06/0299 and LU06/ LU06/0258 24.5 25.8 25.3 25.2 0299 had low positive interactions than the rest of the LU06/0299 19.9 28.5 28.5 25.6 genotypes. Kenya had IPCA score close to zero. LU06/0428 20.1 26.9 15.6 20.9 Bembeke and Maseya showed positive interactions while LU06/0527 19.9 25.9 15.8 25.0 Bunda had negative interaction.

Zondeni 21.5 27.0 24.8 24.4

Kenya 28.5 25.3 28.2 27.3 DISCUSSION Mean 22.4 27.7 21.5 23.9 Genotypes P= 0.45 Results from this study indicated that dry matter content Sites P= 0.01 LSD 0.04 of most new genotypes, particularly LU06/0527, were G x E P= 0.41 comparatively similar to Kenya variety (a released check

CV (%) 24.0 variety), hence suggesting their potential to be accepted by consumers. Dry matter content is an important quality parameter in sweet potato production as it indicates mealiness in the boiled or roasted sweet potato and is a Maseya. On Maseya. On the other hand, Kenya was the property most preferred by consumers (Kathabwalika et least performer at Bunda and Maseya, while LU06/0299 al., 2013). The combination of high dry matter (>25 %) performed poorly at Bembeke. and starch helps in selection of cultivars (Brabet et al., 1999; Lebot, 2009). One of the major challenges for adoption of OFSP is their low dry matter content (Carey Stability of beta-carotene content et al., 1999). These results also suggests that current breeding programmes which aim at producing OFSP with The variations due to genotypes, environment and high dry matter are able to incorporate desirable traits. In interaction between genotype and environment accounted this study, the highest beta-carotene content was for 76.9, 15.2 and 7.9%, respectively, indicating that beta- produced at Maseya followed by Bunda and Bembeke. carotene differences were mainly due to genotype (Table The beta-carotene trend could be attributed to prevailing 6). The decomposition of interaction into principle environmental conditions in the study sites. Maseya is components showed that IPCA1 and IPCA2 accounted located at low altitude and is characterized by high for 78.1 and 21.9%, respectively, as such, IPCA1 was temperatures, high nitrogen and organic matter levels. 324 Afr. J. Food Sci.

Table 6. Analysis of variance according to Additive Main effects and Multiplicative Interactions (AMMI) of beta-carotene (µg/100 g).

Source of variation Degree of freedom Sum of squares Mean square Variation (%) Total 71 364781123.0 5137762.0

Genotypes (G) 7 288288827.0 41184118.0*** 76.9 Environment (E) 2 16240269.0 8120134.0*** 15.2 Reps (within E) 6 22761.0 3794.0

GxE interaction 14 59929311.0 4280665.0*** 7.9 IPCA1 8 49486262.0 6185783.0*** 78.1 IPCA2 6 10443050.0 1740508.0 21.9 Error 42 299954.0 7142.0

***Denotes significant at 1%.

Figure 1. Biplot of IPCA 1 scores against beta-carotene content (μg/100 g) for eight OFSP genotypes grown in three locations. Genotypes: G1=BV/009, G2=Kenya, G3=LU06/0252, G4=LU06/0258, G5=LU06/0299, G6=LU06/0428, G7=LU06/0527, G8=Zondeni.

Bembeke is at high altitude and is characterized by cold carotene at Maseya were in agreement with Rodriguez- temperatures, high soil nitrogen content and low organic Amaya and Kimura (2004) who reported that high matter. Bunda is at medium altitude and is characterized temperatures promote synthesis of carotenoids in tropical by warm temperature, moderate soil nitrogen content and fruit crops. On the contrary, it is also reported that beta- moderate organic matter. These results compare well carotene increases with increasing altitude (Mbwaga et with findings of Ukom et al. (2009) and Nedunchezhiyan al., 2007; Ndirigwe et al., 2007; Manrique and Hermann, et al. (2010) who reported that high nitrogen supply and 2000). The variations within genotypes would be a result organic matter increases beta-carotene content in OFSP. of genetic make-up of the cultivars in the synthesis of Additionally, sweet potato is a tropical crop carotenoids (Rodriguez-Amaya and Kimura, 2004). Some (Nedunchezhiyan et al., 2010), the high levels of beta- genotypes produce more beta-carotene than others due Kathabwalika et al. 325

to the differences in their genetic makeup. For example, ACKNOWLEDGEMENT LU06/0252 produced highest beta-carotene while Kenya consistently produced low levels of beta-carotene. In this This work was funded by Agri-Food Systems Project study, the beta-carotene content values were under International Development Research Center comparatively similar to findings reported by Kapinga et (IDRC). al. (2010) where the OFSP cultivars grown in Eastern and Southern parts of Africa had values ranging from 5 000 to 10 000 µg/100 g. REFERENCES Stability analysis of beta-carotene showed that Bunda Brabet C, Reynoso D, Dufour D, Mestres C, Arredondo J, Scott G and Maseya were favorable environments for genotypes (1999). Starch content and properties of 106 Sweetpotato clones LU06/0428 and BV/009, respectively while genotypes from the World Germaplasm collection held at CIP, Peru. LU06/0299, LU06/0258 and Zondeni were moderately International Potato Center program. Pp.279-286. stable across sites. 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